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A lot of good advice has been given, and I'll just throw in my two cents on top of it. I've changed more timing belts and oil seals that I can recall now, and here's the procedure that I use consistantly.
When changing the front crank seal, the first thing I do is lube all the seals up with synthetic motor oil, put them back in their plastic bags, and then stick them in the freezer for at least 3 hours (preferably overnight). The reason for this is that the metal bands inside each of the seals will shrink a few thousands of an inch due to the temperature drop, and this makes a significant difference in how easy or difficult the seal will be to get in. I also have twice as many seals on hand for the job as there's always a chance that I might damage one in the process. If I bend the outer face of the seal during the installation, I start over with a fresh one.
Once the old seal is removed, I take a scotch-brite pad and clean the cavity for the seal and the shaft too. Even a tiny bit of dried or burned oil crud on the shaft can cause an early seal failure, so I'm pretty anal about getting the shaft as clean as possible. Cleaning the cavity that it mounts into is essential as any dirt or crud here will make the seal insertion more difficult.
When installing the new seal, I take the old seal and turn it around backwards and put it face to face against the new seal. This gives me a surface to push and pound on without damaging the new seal. With a few scraps of wood, usually some 1"x2" or 1"x4" pieces to clear the lower aluminum guard, I tap the new seal into place. I use a standard 20 ounce hammer turned sideways (so that I don't smack the radiator) and tap on the wood blocks. The wood blocks are pushing on the old seal, which in turn presses the new seal into position. Every few taps, I remove the wood blocks and the old seal, check for alignment, and resume the tapping so as to keep it as straight as possible when going in. I try to get the new seal flush with the seal cavity so that all of the edge of the seal is grabbing the aluminum carrier plate cavity and giving it maxiumum grip.
If you observed any scoring on the shaft during the cleaning process, you can mount the new seal up to 6mm deeper in the cavity to get the seal lips turning on a fresh section of shaft. Use caution when recessing the seal, and don't go too far.
Side notes: From the time I remove a seal from the frezer, I try to get it at least half way installed during the first 2 minutes. The seal starts expanding the moment it's in contact with the warm air and my warm hands, so have all your tools, the wood blocks, and the old seal standing by and ready to go. Once it's in half way, I go a bit slower, taking care to get proper alignment and depth.
Be sure that the seal is dripping with oil before you put it in the freezer, and it's essential that the inner lips are very well lubed. You do not want the shaft turning dry on the seal when you start the car. I use synthetic oil since it won't break down over time and this is not an area where you're going to have much oil replentishment (there's no natural oil flow in this area, only a tiny amount pushed through due to crankcase pressure from piston blow-by).
When doing the camshaft seal, I will often not lube the outer edge of the seal where it contacts the aluminum head, as this is often a culprit seal that can pop out of place under elevated crankcase pressure. I've even seen a few that were sealed with RTV on the outer edges (it still had oil on the lips where it contacted the shaft).
Lastly, be sure to clean the ENTIRE crankcase ventilation system as this has a direct effect on how much pressure is put on the seals. You will want to have a clean flame trap, clean tubes & vacuum hoses, a clean nipple on the intake manifold, AND a clean Oil Trap (aka Breather Box, aka Oil Separator, -the big black fist sized box mounted to the block just above the starter). Most people neglect cleaning the Oil Trap, but it merits cleaning out the ports on it every 150,000 miles (it's held to the engine block by two 12mm bolts, and uses a $1 seal 949659 that you can get from FCP Groton). As the oil vapors and droplets pass through the Oil Trap, many collect here and as they dry out in the upper vent port and the lower oil return port which constricts the vent system. This causes elevated crankcase pressure because it slows down the escape of the blow-by gases, and consequently the engine starts bleeding oil out the oil seals. I've had many people come to me, expecting to need oil seal changes due to bleeding seals, but found that the problem was caused by a restricted vent system. They had been cleaning the flame trap and tubes, but the ports on the Oil Trap were constricted and causing the same problem as a clogged flame trap. -oh, and don't ever install the little screens in the flame traps. There's a Volvo Technical Service Bulletin that advises discontinuing their use. Their purpose was to keep a backfire from going from the intake manifold backwards into the crankcase and igniting the oil vapors, but when was the last time you heard a fuel injected engine backfire? The screen is only useful on the carb'd engines which we didn't get in the US markets.
God bless, and I hope the seal installation goes well.
Fitz Fitzgerald.
P.S. Steve, feel free to add any or all of this info to the archives if you'd like.
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